The invention is in the field of electronic reproduction technology and is directed to a device and to the operation thereof for automatically clamping film material onto the recording drum of a reproduction device, for the vacuum control of the recording drum and for releasing the film material exposed by a recording element from the recording drum. In particular, the reproduction apparatus is a color scanner or color recorder.
In reproduction technology, color separations for multi-color printing are produced with color scanners or color recorders. For that purpose, color signals are first acquired by optoelectronic, trichromatic scanning of a chromatic original and these color signals are converted into color separation signals by a color correction. Sheet-shaped film materials, also referred to as film proofs or film sheets are clamped on a recording drum of the color scanner or color recorder and are exposed point-by-point and line-by-line by a recording element that is modulated in brightness by the color separation signals. The exposed film proofs are released from the recording drum and are developed. The developed film proofs are the color separations for the multi-color printing.
The film proofs to be exposed and having different formats can already be present in the form of sheet film material that is taken from a sheet film cassette for clamping or that is cut-off from roll film material situated in a roll film cassette before the clamping.
In traditional color scanners or color recorders, the film proofs to be exposed are manually clamped onto the recording drum and are fixed thereat either with adhesive tape or with a vacuum suction.
It is required for an effective and economical use of a color scanner or color recorder to enhance the efficiency particularly by shortening the preparation and adjustment times at the color scanner as compared to the times required for the actual film exposure. The preparation and adjustment times, for example, can be reduced in that the optimum adjustment parameters for a good reproduction are calculated by an operator in a prior process on the basis of work preparation devices (AV devices) and are stored and are then transferred into the color scanner in a short time immediately before the film exposure. At the same time, as many work steps as possible that are to be normally executed by the operator must be automated, for example the clamping and releasing of the film proofs onto or, respectively, from the recording drum.
Added thereto is the desire to be able to expose film proofs having different formats, particularly large-format film proofs, for, for example, reproduction of posters.
DE-B-22 09 515 already discloses an electronic reproduction device having a means for clamping sheet-shaped recording material onto a recording drum with vacuum suctioning and for releasing the exposed recording material.
The film proofs to be exposed, which are situated in a sheet film cassette, have their registration perforations hooked over registration pins situated on the recording drum with a manually actuatable roller and lever mechanism in the known reproduction device. The vacuum pump is then switched on and the recording drum is turned, as a result whereof the film proofs are pulled from the sheet film cassette, are wound around the rotating recording drum and are fixed on the drum surface by the vacuum. After the exposure, the film proofs are released and are in turn conveyed back into the roll film cassette by the roller and lever mechanism.
The recording drum is a hollow cylinder that is closed by covers. Shaft journals with which the recording drum is rotatably seated at the device carrier of the reproduction device are secured to the covers. The wall of the hollow cylinder is provided with suction holes for suctioning the film proofs against the drum surface. The suction holes are in communication with the interior of the drum. One shaft journal is hollow, a suction channel arising as a result thereof which connects the drum interior to a stationary vacuum pump via a rotary transmission leadthrough secured to the shaft journal and via a stationary suction line.
The device known from DE-B-22 09 515 has the disadvantage that only film proofs provided with registration perforations and having given formats can be clamped and that the clamping and release can only occur with the collaboration of the operator.
U.S. Pat. No. 4,268,841 discloses an electronic reproduction device that already comprises an apparatus for automatically clamping sheet-shaped recording material onto a recording drum, for vacuum suctioning of the recording material against the recording drum and for the automatic release of the exposed recording material from the recording drum. The sheet-shaped recording material is automatically conveyed from a supply station via a conveyor means to the recording drum, is wound around the recording drum with the assistance of an annular channel between drum surface and housing 1 and is fixed thereat by vacuum suctioning. After the exposure, the recording material is likewise automatically released from the recording drum and is supplied to an exit opening in the device for further-processing. The generated surface of the recording drum is provided with suction holes arranged in a rotational direction that are connected to a stationary vacuum pump via the interior of the recording drum and via a suction line in the shaft. A vacuum control means with which the vacuum for the suction holes is switched on and off or can be set to an intermediate value is situated in the suction line.
The device disclosed by U.S. Pat. No. 4,268,841 has the disadvantage that only sheet-shaped recording material can be clamped and released and that no special measures are recited for the reliable, fold-free clamping of recording material of different formats which guarantee a friction-free, automatic execution.
Both known apparatus have the further advantage that all suction holes of the recording drum are simultaneously charged with vacuum when the vacuum pump is switched on at the beginning of the clamping process. High vacuum losses arise as a result thereof, particularly given small-format film proofs, since only a small number of suction holes are covered by the film proof. A reliable clamping of the film proofs during the exposure time wherein the recording drum rotates at high speed is then not assured as a consequence of the high vacuum losses. The suction effect and, thus, the fixing of the film proofs can in fact be improved by installing a vacuum pump having a higher nominal output; this, however, would be costly.
It is already known for reducing the vacuum losses to seal the suction holes that are not respectively covered by the film proof clamped on at the moment with adhesive strips or to employ a recording drum wherein the non-covered suction holes are automatically closed with valves. The sealing of the suction holes with adhesive strips is time-consuming and sealing them by automatically operating valves is involved and unreliable.
It is likewise already known to subdivide the recording drum into individually connectable vacuum chambers with transverse walls. In this case, a reduction in the vacuum losses can be achieved in that only those vacuum chambers are respectively activated that momentarily participate in the fixing of the film proofs based on the axial format length.
DE-A-32 30 676 already discloses a vacuum clamping means that uses a combination of pneumatic and mechanical components for fixing sheet-shaped recording material on a recording drum. The suction holes of the recording drum are combined into at least two groups, each of these encompassing one or more rows of suction holes connected to one another. The individual suction hole groups are in communication with one another via lines that can be disconnected with valves. At least one group is connected to a stationary vacuum generator. What is achieved by adding individual suction hole groups or suction hole rows is that recording material of various formats can be clamped without high vacuum losses. Means for controlling the valves and for conveying the recording material to or from the recording drum are not recited.
The apparatus disclosed by DE-A-32 30 676 thus has the disadvantage that the feed of the sheet-shaped recording material must ensue manually and that the switching of the suction hole groups or suction hole rows does not ensue automatically dependent on the clamping and release event and/or on the respective format of the recording material to be clamped on.
The tendency in reproduction technology is toward the employment of unperforated roll film material and to cut off the respectively required film lengths from the roll film material and to clamp it. Added thereto is the desire to be able to clamp and release arbitrary formats. Practice has shown that it is difficult to clamp, in particular, large-format film proofs on the recording drum exactly and fold-free. The exact and smooth clamping of the film proofs, however, is an indispensable prerequisite for the exposure of exactly registered color separations and for the production of qualitatively high-grade multi-color prints.